1. Field of the Invention
The present invention relates generally to a method and a system for inspecting a microprocessor-based unit or component thereof. More specifically, the invention relates to a method and system for inspecting a microprocessor containing control unit, which as an automotive device control unit, such as an engine control unit, a brake control unit, a suspension control unit and for forth, and particularly for inspecting hardware of the control unit for detecting defective unit.
2. Description of the Background Art
In the recent automotive vehicles, various electronic control units, such as an engine control unit for controlling fuel injection, spark ignition timing and so forth, are installed for optimizing performance of the vehicular devices to be controlled. Such control units have been disclosed in the Japanese Patent First (unexamined) Publication (Tokkai) Showa 61-34334.
In manufacture of such control units, hardware has to be checked or inspected before shipping. Conventionally, one of methods of inspection is to apply a dummy load corresponding to a predetermined condition to the control unit to receive a control signal output from the control unit in response thereto. The control signal is compared with a reference value which represents the control signal value when the control unit operates in normal condition. In another method, an inspection program is installed in the control unit which is also provided with an input port for inputting inspection commands and an output port for outputting data indicative of the result of execution of the inspection program. An externally installed inspection apparatus receives the output of the control unit and compares its with a reference signal to check whether the output from the control unit indicates a normal value as represented by the reference signal.
The former method is economical in the viewpoint of cost. However, in order to check the control unit subjecting inspection, a relatively large number of inspection data are to be processed for obtaining the output to be compared with the reference value. This makes it difficult to identify a faulty component even when a defective control unit is detected. Furthermore, since the control unit must process a large number of data for obtaining the output to be checked, process time in the control unit can be long to require substantially long inspection period for each control unit. This clearly drops the efficiency of inspection. On the other hand, since the latter method is operated by the inspection program installed in the control unit, which uses a program specifically designed for inspection, it becomes easier to troubleshoot a faulty element based on the output. Furthermore, once a special inspection program may be optimized for checking operation of necessary component, process time can be minimized to shorten the inspection period. However, in order to install the inspection program, additional memory area is required and this makes the cost of the control unit expensive.
In addition, in either method, when the specification of the control unit is changed, substantial change of data and process, such as change of program, may become necessary.